The idea of the conjecture is that you define an $$n$$-sided die by sampling uniformly with replacement $$n$$ numbers from $$1, 2,3,\dots,n$$ as the numbers on the sides, with the constraint that the numbers have to add up to $$n(n+1)/2$$. Rolling such a die $$M$$ times samples $$M$$ observations from a distribution on $$1,2,3,\\dots, n$$ with mean $$(n+1)/2$$.  You construct three such dice, $$A$$, $$B$$, and $$C$$.  Their distributions have the same mean, so the $$t$$-test would have no ability to distinguish data from the three distributions, no matter how large $$M$$ was. But the Wilcoxon test probably would. It’s assumed, but not yet proved, that the probability of a tie according to the Wilcoxon test goes to zero as $$n\to\infty$$.
The interesting conjecture is that if you see $$A$$ beat $$B$$ and $$B$$ beat $$C$$ according to the Wilcoxon test, the probability that $$A$$ beats $$C$$ goes to 1/2 as $$n$$ goes to infinity.   That is, given equal means, the Wilcoxon test is basically as non-transitive as possible.